滑动窗口
class Solution {
public int lengthOfLongestSubstring(String s) {
if (s.length()==0) return 0;
HashMap<Character,Integer> map = new HashMap<Character,Integer>();
int max = 0;
int left = 0;
for(int i = 0; i< s.length(); i++){
if(map.containsKey(s.charAt(i))){
left = Math.max(left,map.get(s.charAt(i))+1);
}
map.put(s.charAt(i),i);
max = Math.max(max,i-left+1);
}
return max;
}
}